One known example of a photovoltaic device used in a solar cell that converts the energy from sunlight into electrical energy is a thin-film silicon-based photovoltaic device comprising a photovoltaic layer formed by using a plasma enhanced CVD method or the like to deposit thin films of a p-type silicon-based semiconductor (p-layer), an i-type silicon-based semiconductor (i-layer) and an n-type silicon-based semiconductor (n-layer).
Advantages of thin-film silicon-based solar cells include the comparative ease with which the surface area can be increased, and the fact that the film thickness is approximately 1/100th that of a crystalline solar cell, meaning minimal material is required. As a result, thin-film silicon-based solar cells can be produced at lower cost than crystalline solar cells. However, a drawback of thin-film silicon-based solar cells is the fact that the conversion efficiency is lower than that of crystalline solar cells. In this technical field, improving the conversion efficiency is a very important task.
For example, in patent citation 1 and patent citation 2, the band gaps of the p-layer and the n-layer are widened by adding nitrogen to the p-layer and n-layer, thereby improving the conversion efficiency by increasing the open-circuit voltage.
Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 2005-277021
Patent Citation 2: Japanese Unexamined Patent Application, Publication No. 2006-120930